1. Technical Field
The present invention relates to a staple-former in a stapler in which staples are driven by a driver blade into a workpiece, preferably a sheaf of paper. The stapler contains a staple magazine in which longitudinally extended staple blanks are stored. The staple blanks are advanced onto an integral bending die by a feed device contained in the stapler. The bending die has an upper support surface over which the staple blanks are bent by a staple-former into staple shape. This staple shape includes a first and a second leg with an intermediate crown portion. The staple-former has a first leg-bending part and a second leg-bending part with an intermediate crown-forming part that exhibits a stamping surface. The formation of a staple is accomplished by the staple-former being driven by a drive device that is integrated into the stapler from an starting position in a staple-forming motion in a direction that is transverse to the direction of extent of the support surface. During this motion, the staple-former is brought against the bending die, whereupon the leg-bending parts over the bending die bend the staple blank into a staple shape. In a continuation of this motion, the staple-former is advanced a distance such that the stamping surface of the crown-forming part presses the crown portion of the staple blank against the support surface. After this, the staple-former is reciprocated by the drive device back the starting position and the bent staple that has been formed is fed forward to the driver blade.
2. Background of the Invention
Staple-formers of the type described above are generally known. Such a staple-former is exemplarily described in the Swedish patent application SE 9201230-1. A disadvantage of earlier staple-formers is that they require extremely precise regulation of the staple-forming motion, since it is very important that the staple-former undergo reciprocation within an extremely narrow tolerance range. If reciprocation occurs too early, the crown-forming part will not press the staple crown against the bending die, and the staple blank will not be bent sufficiently and this often causes the stapler to jam. If reciprocation occurs too late, the crown-forming part will strike the bending die with great force, which damages the staple while at the same time causing the staple-former and drive device to wear much more rapidly. To counteract the aforesaid disadvantages, solutions have previously been proposed in which the stapler is equipped with damping devices that damp the staple-forming motion before reciprocation occurs. These devices are often complicated and expensive to fabricate, and they fail to solve the problems that arise when reciprocation occurs too early.
Another disadvantage of existing staple-formers is that, since they are usually driven by the same drive device that drives the driver blade, the staple-former must be adjusted precisely in relation to the driver blade, which can often be an extremely difficult task to perform.
The present invention overcomes these disadvantages by means of a staple-former of a type in which the crown-forming part is displaceably connected to the staple-former by means of an intermediate biasing means, also referred to as an elastic element and/or a take-up device or means. In a preferred embodiment, the elastic element takes the form of a leaf spring bent into a hairpin shape. Further in this preferred embodiment, the crown-forming part is displaceably connected to the staple-former by means of a guide arrangement. Still further, the staple-former exhibits an integrated driver blade. The biasing means or elastic element is configured or selected so that the biasing force exerted thereby is sufficiently high to maintain the crown-forming part in an extended position through out the bending of a staple blank over the bending die, but also sufficiently weak to permit the crown-forming part to retract into the body of the staple-former when the staple bending process has been completed, but the staple-former continues to be driven toward the bending die.